1. Magnetization Characteristics of DC Shunt … MANUAL/EM-I LAB MANUAL FINAL...NSCET LAB MANUAL DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING 1. Magnetization Characteristics

NSCET LAB MANUAL

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

1. Magnetization Characteristics of DC Shunt Generator

Aim:

To conduct an experiment on a D.C shunt generator and draw the magnetization characteristics

(OCC) and to determine the critical field resistance and critical speed.

Apparatus:

Circuit diagram:

3 point starter

DPST Switch L F A +

DPST Switch

+

230 V DC

Supply

400Ω/

1.7A

F

M

A

(0-

500)V

+

A (0-2)A

− MC

F

DC

Excit-

F

− Fuse

FF

−

Fuse

S. No Apparatus Type Range Qty

1 Voltmeter M.C 0-250/500V 1

2 Ammeter M.C 0-1/2A 1

3 Rheostats Wire wound

400/1.7A 1

4 Tachometer Digital 0-9999 1

+

V

−

G

A

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Shunt Field Resistance (Rsh):-

+

230 V

DC

Sup-

DPST FUSE

400Ω/1.7

+

A (0-2A)

F

FF

+

V (0-250V)

Theory: Open circuit characteristics or magnetization curve is the graph be-

tween the generated emf and field current of a dc shunt generator. For field cur-

rent is equal to zero there will be residual voltage of 10 to 12V because of the

residual magnetism present in the machine .If this is absent there the machine

can not build up voltage to obtain residual magnetism the machine is separately

excited by a dc source from OCC we can get critical field resistance and critical

speed.

Critical field resistance: It is the resistance above which the machine cannot

build up emf.

Critical speed: It is the speed below which the machine cannot build up emf.

Procedure:

1. Connections are made as per the circuit diagram.

2. Start the motor and bring it to rated speed..

3. The switch SPST is opened and If=0

4. For the different values of excitations (If) the generated voltage (Eg)from

the voltmeter is taken at rated speed, with increasing and decreasing orders.

5. Calculate average Eg from increasing and decreasing orders.

6. A graph is drawn between Avg Eg & If. From the graph (OCC) Critical

field resistance and critical speed are calculated.

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)

R

Rf

A

Q

Tabular column:

S.NO Field current

If

Generated Voltage (Eg) Average Eg

Increasing Decreasing

Graph:

Eg (V

O C P If (A)


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Critical field resistance (Rc) = OA/OC

Field resistance (Rf) = OR

The maximum voltage the Generator can induce

With this field resistance. = OM

Critical Speed = PQ/PR * N

Result:


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2. BRAKE TEST ON DC SHUNT MOTOR. DETERMI-

NATION OF ITS PERFORMANCE CURVES

Aim: To conduct brake test on DC Shunt motor. And to determine its performance curves.

Apparatus: S. No Equipment Range Type Qty

1. Voltmeter 0-250V M.C. 1

2. Ammeter 0-20A M.C 1

3 Ammeter 0-1/2A M.C 1

4 Rheostat 400/1.7A Wire wound 1

5. Tachometer Digital type 1

6. Connecting wires


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Circuit diagram:

(0-20)A 3 point starter

DPST Switch MC L A F

+ A

+

400Ω/ + S1 S2

1.7A A (0-2)A 230 V V (0-250)V MC

DC − MC −

Sup- F M

A

FF

− Fuse


Theory: When if is required to determine directly efficiency if comparatively small

motors, the motor is loaded directly by means of Mechanical Break. Hence in the

case of shunt motor there is no drastic change in speed. The Torque

T = (S1 ~ S2) g. r – Nm. where S1 S2 is the spring balance reading, r = Break drum

Radius and g=9.81.

P = Power developed. Efficiency of DC motor = Po/ Pi x 100

Procedure:-

01. Make Connections as per the circuit diagram.

02. Start the motor with the help of the starter.

03. Then bring the motor to rated speed by adjusting field rheostat.

04. Put the mechanical load on the motor in steps and note down correspond-

ing readings of all meters.

05. Do calculations accordingly.

Tabular columns :

S.No Voltage

(V)

Current

(I)

Spee

d

(N)

Spring

Balance

Readings

Torque=

9.8 1(S1 ~

S2) .r -Nm

Pout =

2 nT/60

-Watts

Pin =

Vi - Watts

Eff =

op/ip

x100.

S1 S2


EXPECTED GRAPHS:

Y

Ta vs Ia.

X

N

0 Ia Y

N vs Ia

T T sh

Ta

0 X

Ia


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Y

N vs T

X

η

Y

O/P

Vs O/P

Result:

T


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S1 S2

3. BRAKE TEST ON DC COMPOUND MOTOR DE-

TERMINATION OF PERFORMANCE CURVES

Aim: To conduct brake test on dc compound motor.

Apparatus:

S. No Equipment Range Type Quantity

1 Voltmeter (0-250V) M.C. 1 No

2 Ammeter (0-20A) M.C 1 No.


4 Tachometer digital 0-9999 1No

5 Connecting wires

Circuit diagram:

Cumulative:

DPST Switch

(0-20)A

MC

3 point starter L A F

+ A

Y

+ 400Ω/ +

230 V

DC

Sup-

V (0-250)V

− MC

A YY

M

1.7A A (0-2)A

− MC

F

AA

FF

− Fuse

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S1 S2

Differential:

(0-20)A 3 point starter

DPST Switch +

MC −

L A F + A

YY

+ 400Ω/ +

230 V

DC

Sup-

V (0-250)V

− MC A Y

M

1.7A A (0-2)A

− MC

F

AA

FF

− Fuse

Theory: A Compound motor has a shunt field winding as well as series field winding. If the

series field mmf and shunt field mmf help each other it is a cumulative compound

motor. If the series and shunt fields appose each other it is a differentially com-

pound motor. The operation of differential compound motor is unstable In a cumu-

lative compounded motor the fluxes are add each other at light loads the shunt field

is stronger than series field so motor behaves shunt motor. At high loads series

field is stronger than shunt field so the characteristics like nearly to series motor.

Procedure: 1. Connections are made as per the circuit diagram.

2. Start the motor with the help of the starter.

3. Then bring the motor to rated speed by adjusting field rheostat.

4. Put the mechanical load on the motor in steps and note down all the meter read-

ings.

NSCET LAB MANUAL


Tabular columns:

s.no Voltage (V)

Current (I)

Speed

(N) Spring

balance readings

Torque=

9.81xS1

~S2xr -

Nm

Output

power

2πNT/60-

Watts

Input

power

VI-

Watts

Efficiency

Pout/P in

x 100.

S1 S2

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Graph: Draw graphs O/P Vs Speed, Current, Torque, Efficiency.

Y

Cum

Diff

N

0 X T

N vs Ia

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X

Diff

T

Cum

0 Ia Y

T vs Ia

Y

N vs T

Cum

Diff

T

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X

Y

Vs O/P

Result:

η Cum

Diff

O/P

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4. LOAD TEST ON DC SHUNT GENERATOR.

Aim: To conduct a load test on the given DC Shunt generator and to obtain the

performance characteristics.

Apparatus required:

1 Ammeter 0-20A, MC 1

0-1A, MC 1

0-5A MC 1

2 Voltmeter 0-250V, MC 1

0-30V, MC 1

3 Rheostat 400/1.7A 1

4 Rheostat 100/5A 1

5 Load 3 Kw / 220V 1

6 Tachometer 1

5 Connecting wires

Circuit diagram:

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Armature Resistance (Ra):-

(0-30V)

Theory: . By conducting load test on DC shunt generator we can get load characteris-

tics i.e, Internal & External characteristics. By exciting the m/c, the field current

increases and voltage build up. After the machine has attained 220V the rated load

is switched on. With increase in load, the voltage will be dropped

Procedure: 1. Connections are made as per the circuit diagram.

2. Start the machine with the help of starter and bring to rated speed by vary-

ing field rheostat of motor, then by varying field rheostat of the generator

set the rated voltage of the generator.. Then close the DPST switch of the

load and increase the load by step 0.125Kw, up to full load of the generator.

3. Note down all the meter readings at every step.

4. Do necessary calculations.

Observations:

S no

IL, in amps

If , in amps

Ia= IL+if in amps

Vt in volts

Ia Ra in volts

EG = Vt + IaRa in volts

DPST FUSE

+ +

100Ω/5A A (0-5A)

−

230 V

DC

Supply

A

AA

+

V

−

−

M

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Graph:

X

Y

E& vs I

E&V vs I

Result:

E&

Internal

External P

I

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5. LOAD TEST ON DC SERIES GENERATOR

Aim: To conduct load test on the given DC series generator and to obtain its per-

formance characteristics.

Apparatus required:

S.NO Equipment Range Type Qty

1 Ammeter. 0-20A M.C. 1

0-5A MC 1

2 Voltmeter. 0-250V M.C 1

0-30V MC 1


100/5A Wire wound 1

4 Load 5,Kw 1

5 Tachometer 0-9999 Digital 1

Circuit diagram:-

3 point starter

(0-20A)

DPST Switch L A +

230 V

DC A Sup-

M

F

400Ω/ YY 1.7A

Y

F A

G

DPST Switch + −

A

+

V (0-250v)

− AA

FF AA

Resistive Load

− Fuse


NSCET LAB MANUAL


+

230 V

DC Sup-

DPST FUSE

100Ω/5A

+

A (0-5A)

A +

M V (0-30V)

AA

Series Field Resistance (Rse):-

+

230 V

DC Sup-

DPST FUSE

100Ω/5A

+

A (0-5A)

Y

YY

+

V (0-30V)

Theory: The load characteristics curve of DC series generator shows the relation

b/w its terminal voltage and load current. The characteristics are rising in

nature and excitation increases with load. At large values of load current,

the terminal voltage must be start decreasing owing to the saturation of the

machine iron & rapidly increasing voltage drop of armature and armature

resistance.

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Procedure: 1. Make connections as per the circuit diagram.

2. Adjust the speed of the motor to its rated value using field rheostat.(motor).

3. Connect the load to generator with the help of load box, and increase the

load 0.125Kw at every step and note the corresponding readings.

4. Plot the graph b/w terminal voltage Vs current and generated voltage Vs

armature current.

Observations: Speed of the motor, N =

Sno Terminal voltage, in volts

Load current, IL=Ia=Ise in amps

IaRa In volts

IaRse In volts

Eg=V+IaRa+IaRse In volts

Graph: Plot the graph b/w terminal voltage and load current by taking ‘V’ on Y-

axis and ‘IL’ on X-axis, and Eg on Y axis and Ia on X axis.

X

Eg & V

Y

Eg & V vs Ia= Ise

Result:

OCC

Internal

External

Ia = Ise

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(0-2A)

6. SPEED CONTROL OF DC SHUNT MOTOR

Aim: To conduct speed controls on DC shunt motor.

The methods are

1. Armature voltage control method 2. Flux control method

Apparatus:

S.No Equipment Range Type Qty

1 Ammeter 0-5A 0-2A

MC MC

1No 1No

2 Voltmeter 0-250V MC 1No

3 Rheostats 100/5A Wire wound 1NO

400/1.7A Wire wound 1No

4 Tachometer 0-2000rpm Digital 1No

5 Connecting Wires LS

Nameplate Details (To be noted Down from the Machine)

Circuit diagram:

DPST FUSE

+

100Ω/5A

L A F

400Ω/1.7A

230 V

DC

Supply

+

(0-250V) V

−

+ +

A (0-5A) A

− −

A F

M

AA

FF

−

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+

230 V

DC

Sup-

DPST FUSE

100Ω/5A

+

A (0-5A)

A +

M V (0-30V)

AA

Theory:

i) Armature voltage control method: For a load of constant Torque, the speed is proportional to the applied to the arma-

ture. Therefore speed voltage characteristic is linear and is a straight line. As the

voltage is decrease across the armature the speed falls. This method gives speeds

less than rated speeds.

Eb α ΦN Eb α N

V-Ia(Ra+R) α N

As the voltage is decreased speed decreases.

ii) Flux Control Method: With rated voltage applied to the motor, the field resistance is increased i.e field

current is decreased. I t is observed that speed increases.

Eb/Φ α N N α Eb/If

The characteristics If Vs N is inverse (or) if it is hyperbola.

Procedure:

i) Armature Voltage Control Method

1) Make connections as per the circuit diagram.

2) Show the connections to the lab instructor.

3) Keeping both rheostats at minimum, Start the motor with the help of starter and

by adjusting field rheostat bring the motor to rated speed.

4) By increasing armature circuit rheostat in steps note down voltage, Ia and speed

at every step.

5) The corresponding graph is draw between armature Voltage Vs speed.

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ii) Flux Control method:

1) The machine run at its rated speed and rated voltage obtained.

2) The voltage is kept constant and for different values of field current the

speed are noted.

Tabular Column: Armature Voltage Control Method:

S.No Armature

Voltage in

volts

Armature

current=Ia

in amps

Speed

in RPM

Eb=V-IaRa in

volts

Flux Control Method:

S.No Field Current in amps Speed in RPM

Expected graphs:-

Y

N

O X

If(I)

N Vs If

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Y

N

O X

Va(V)

N Vs Va

N vs Va(Armature voltage)

Result:

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+ + A

−

+ 400Ω/

1.7A

230 V

DC

Supply

A (0-2)A +

V

−

(0-250)V

MC A

MC −

F M

AA

FF

−

6. SWINBURNE’ S TEST ON DC SHUNT MACHINE

PREDETERMINATION OF EFFICIENCIES

Aim: To perform no load test on dc motor and to predetermine the efficiencies of

the machine acting as a motor and generator.

Equipment:

S.No Apparatus Type Range qty

1 Voltmeter MC 0-250v 1

2 Voltmeter MC 0-30V 1

3 Ammeter MC 0-5A 1

4 Ammeter MC 0-2A 1

5 Rheostats Wire wound 400/1.7A 1

Wire wound 100/5A 1

Circuit diagram:

DPST Switch

Fuse

(0-5)A

MC 3 point starter

L A F

NSCET LAB MANUAL


+ DPST Switch

100Ω/5A +

A (0-5)A

MC

230 V

DC Sup-

ply

−

A

M

AA

+

V

−

−

Circuit diagram to find out Ra:

(0-30)V

MC

Theory:

Fuse

It is simple indirect method in which losses are measured separately

and the efficiency at any desired load can be predetermined. This test applicable to

those machines in which flux is practically constant i.e. shunt and compound

wound machines. The no load power input to armature consist iron losses in core,

friction loss, windage loss and armature copper loss. It is convenient and economi-

cal because power required to test a large machine is small i.e. only no load power.

But no account is taken the change in iron losses from no load to full load due to

armature reaction flux is distorted which increases the iron losses in some cases by

as 50%

Procedure:

1. Make connections as per the circuit diagram.

2. Show the connections to the lab instructor.

3. Keeping both rheostats at minimum, Start the motor with the help of starter and

by adjusting field rheostat bring the motor to rated speed.

4. Note down all the meter readings at no load..

5. Do necessary calculations and find out the efficiency of the Machine as a motor

and as a generator.

6. Draw the graphs between output Vs efficiency of the Machine as a generator and

as a motor.

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Generator

Motor

Observations:

IL IF IA V N

For Ra

S.NO V I Ra=V/I

Expected graphs:-

η

O Out-

Efficiency Vs Output

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Tabular Column to find out efficiency:

GENERATOR:

S.No Voltage

in volts

Load

Current

in amps

Armature

Current Ia =

(IL+If)

Armature

Cu loss=

Ia XIaXRa

Total losses

Wt=Wc+

IaXIaXRa

Input-

VxIL

Output-

Input-total

losses=

VxIL-Wt

=

Outpu

Input.

t

Motor:

S.No

Voltag

e in

volts

Load

Current in

amps

Armature

Current

Ia =(IL-If)

Armature

Cu loss= Ia

XIaXRa

Total

losses

Wt=Wc+

IaXIaXRa

Output=

VxIL

Input=output

+total loss-

es=

VxIL+Wt

=

Outpu

Input.

t

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Model calculations:

No load input=V IL

No load armature copper losses =Ia 2 Ra =(Il –If)2 Ra

Constant losses Wc=V l–(Il-If )2 Ra

Efficiency as a motor:

I= Assumed load current

Motor i/p=VI

Ia=IL-If

Motor armature losses=I2a .Ra

Total losses=I2a Ra+ Wc

Efficiency of motor= VI- I2a Ra+ Wc / VI x 100

Efficiency as generator:

I=assumed load current

Generator O/P =VI

Generator armature cu. Losses= I2a .Ra

Total losses= I2a Ra+ Wc

Efficiency of generator=VI / VI+ I2a Ra+ Wc

Results:

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7. LOAD TEST ON COMPOUND GENERATOR

Aim: To conduct load test on DC compound generator and to determine its

characteristics.

Apparatus:

S. No Equipment Range Type Qty

1. Voltmeter 0-250 V M.C. 1

2. Ammeter 0-2A 0-20A

M.C. M.C.

1 1

3. Rheostats 400/1.7A Wire wound 2

4. Tachometer Digital 1

5 Connecting wires

Circuit diagram for cumulative compound generator:

DPST Switch

+

230 V

DC A

400Ω/

1.7A

F

400Ω/

1.7A

F

(0-2A)

+ A

−

A

(0-20A)

+ − A

Y

YY

+

DPST Switch

Sup- M

AA

FF FF

G V (0-250v)

− AA

Resistive Load

− Fuse


+ − + −

400Ω/

1.7A

A A

YY

Y

F A

G

+

V

−

(0-250v)

FF AA Resistive Load

100Ω/5A

A (0-5A)

M

Circuit diagram for differential compound generator:

DPST Switch

+

230 V

DC A Sup-

M

400Ω/

1.7A

F

(0-2A) (0-20A) DPST Switch

AA FF

− Fuse


(0-30V)

AA


+

230 V

DC

Sup-

DPST FUSE

100Ω/5A

+

A (0-5A)

Y

YY

+

V (0-30V)


NSCET LAB MANUAL


Theory:

D.C. Compound generator consists of both series and shunt field wind- ings. The shunt and series fields can be connected in two ways.

1. Short shunt.

2. Long shunt.

When the MMF of series field opposes the MMF of shunt field, the gener-

ator is differentially compound. The terminal voltage decreases sharply with in-

creasing load current. Evidently this connection is not used.

In cumulative compound the connections of the two fields are such that

their MMF’s added and help each other. If the series field is very strong, the termi-

nal voltage may increase as the load current increases and it is called over com-

pounding. When terminal voltage on full load and no load are equal, it is known as

flat compounded generator. If the series field is not strong, the terminal voltage

will decreases with increase in load current (under compound)

Procedure:

1. Connections are made as per the circuit diagram.

2. The machine is run at rated speed and the rated voltage is obtained by vary-

ing field excitation

3. There the switch is closed so that load is connected across the generator.

4. Increase the load step by step with 0.125Kw and note down all the meter

readings and calculations are made accordingly and the characteristics are

obtained.

5. Plot graph for internal external characteristics.

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Tabular Column:-

S.No IL , Amps VL Volts If , Amps Eg = vl+IA (rn+rsc)

Model graphs:-

Internal characteristics

Y

Cumulative

Differential

E (V)

O

X

Ia (A)

E (V) Vs Ia

NSCET LAB MANUAL


External characteristics

Y

Cumula-

Differential

V

O

X

Ia (A)

V Vs Ia

Result:-

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8. FIELDS TEST ON TWO IDENTICAL DC SERIES

MACHINES

Aim: To determination the efficiency of two mechanically coupled series ma-

chines by conducting field’s test.

Apparatus:

S.No Equipment Range Type Qty

1. Voltmeter 0-250V 2-30V

M.C. MC

3 1

2 Ammeter 0-20A 0-5A

M.C. M.C.

2 1

3. Resistive load 5Kw

4. Connecting wires

Circuit diagram:

2 point starter (0-20A)

DPST Switch

+ +

(0-20A) L A

A −

DPST Switch + −

A

Y Y

230 V

DC Sup-

+ YY

V (0-250v) A

A +

YY V

(0-250v)

− M G

−

AA AA

Resistive Load

− Fuse

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+

230 V

DC

Sup-

DPST FUSE

100Ω/5A

+

A (0-5A)

A +

M V (0-30V)

AA


+

230 V

DC

Sup-

DPST FUSE

100Ω/5A

+

A (0-5A)

Y

YY

+

V (0-30V)

Theory: This test is applicable for two series machines which are coupled mechani-

cally. Series machines cannot be tested on no load conditions due to dangerous

high speeds. One machine normally run as motor and drives generator whose out

put is wasted in a variable load R. The fields of two machines are connected in se-

ries in order to make iron losses of both the machines equal.

Model calculations: Generator output = V3.I2 Watts. - - - - - - - - - (1)

Total input = V1.I1 Watts. - - - - - - - - (2)

Total losses Pt of both machines = ( V1.I1)-(V3.I2) Watts - - (3)

Motor Field Cu loss = I1.I1.Rsem - - - - - - - - - - (4)

Motor Armature Cu loss = I1.I1.Ram - - - - - - - - - - -(5)

NSCET LAB MANUAL


Genera-

Motor

Generator Field Cu loss

Generator Armature Cu loss

P2,Total Ra and Se ,Cu losses

=

=

I1.I1.Rseg - - - - - - - - - - (6)

I2.I2.Rag - - - - - - - - - - - -(7)

Of both machines = (4)+(5)+(6)+(7)- - - - -- - --(8)

Ps, Stray losses of both m/c = (Pt-P2) Watts - - - - - - - - -(9)

Ps/2, Stray losses of each m/c = (Pt-P2)/2 Watts- - - - - - - - -(10)

Efficiency calculations for Generator:-

Output of Generator =V3 . I2 Watts---------------(11)

Stray losses of Generator = (Pt-P2)/2 Watts ----------(12)

Field Cu loss of Generator. = I1 . I1 .Rseg----------------(13)

Armature Cu loss of Generator. = I2 .I2 .Rag------------------(14)

Input to Generator. = (11)+(12)+(13)+(14)-------(15)

Efficiency of Generator =Output/Input =(11)/(15)

Efficiency calculations for Generator:-

Motor in put . =V2 .I1 Watts----------------(16)

Motor Field Cu loss = I1 .I1.Rsem-----------------(17)

Motor Armature Cu loss =I1 . I1 .Ram-----------------(18)

Motor Stray losses =(Pt-P2)/2 Watts------------(19)

Motor Output =(16)-(17)+(18)+(19)------(20)

Efficiency of Motor =Output/Input=(20)/(16)

Model graphs:-

η

O Out-

Result: By conducting the field’s test we found the efficiency of series machines

(motor and generator).

NSCET LAB MANUAL


9. REGENERATIVE (OR) HOPKINSON’S TEST

Aim : To conduct a Hopkinson’s test on a two similar D.C shunt machines and

find out the efficiency.

Apparatus Required:

S.no Equipment Range Type Qty

1 Volt meter 0-250V M.C. 1

2 Ammeter 0-20A 0-2A

M.C M.C

2 2


4 Connecting wires

Name Plate Details (To be noted Down from the Machine)

Circuit Diagram:

3 point start-

+ (0-2A)

DPST Switch +

L A F

400Ω/

1.7A

+

V −

A MC

−

+ 400Ω/

230

V

DC

+ (0-230)V

V MC A −

M

AA

+

(0-2)A

− A

MC

F

(0-500)V

MC (0-20)A

A MC

− A

M

AA

1.7A

F

FF

FF −

Fuse

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+

230 V

DC Sup-

DPST FUSE

100Ω/5A

+

A (0-5A)

A +

M V (0-30V)

AA

Theory:

Hopkinson’s test is also called as regenerative test or back-to-back test. It is

an indirect test or full test, which is used to determine the efficiency of the two

identical shunt machines. The two machines are mechanically coupled and are also

adjusted electrically that are of then run as motor and other as a generator. The

two-shunt machines are connected in parallel. The power input from the mains is

only that needed for supplying the losses of the two machines. The two machines

can be tested under full load conditions (for determining the efficiency and maxi-

mum temperature rise).

Procedure:

1. Connected the circuit as per the circuit diagram.

2. Keep the field regulator minimum resistance position and start the motor by

using starter, Keeping S.P.S.T switch open.

3. Adjust the regulator on generator side until the rated voltage equal to both

in magnitude and polarity as that of main supply. i. e; voltmeter reads zero.

4. The S. P. S.T switch is closed to parallel the machines, by adjusting the re-

spective field regulators, any load can how be thrown on to machines.

5. Calculate efficiency by applying load.(changing excitation)

Observations:

S. No Input Volt-

age in volts Input Cur-

rent=I1

Gen Ia=I2 Gen If=I3

Motor If=I4

NSCET LAB MANUAL


To find out efficiency:

Motor:

S. No Motor

input

Motor

Armature

Cu loss

Motor

Field

Cu loss

Stray

loss

Total

losses

of motor

Out put

Of Mo-

tor

of Mo- tor

Generator:

S.

No Generator

output

Generator

Armature Cu loss

Generator

Field Cu loss

Stray

loss

Total

losses of generator

Input

Of generator

of

generator

Calculations: Armature Resistance of each machine =Ra

Generator Armature cu loss =I1 x I2 x Ra Watts. Motor

Armature cu loss =(I1 + I2)(I1 + I2)Ra Watts.

Armature power input to the set. =VL x I1 Watts.

Ps, Stray losses of both machines = VL x I1 Armature Cu loss of

(Gen +Motor)

Stray losses of each machine = Ps/2

Efficiency of Generator:

Generator output =VL . I2 Watts

Generator Losses Pg = V.I3 + I2 x I2+(Ps/2)

Efficiency of Generator =( VL .I2 )/ (VL .I2 +Pg)

Efficiency of Motor :

Motor in put: =VL (I1 +I2 +I4).

Motor losses Pm =(I1 +I2)(I1 +I2)Ra +VxI4 +Ps/2 .

Motor Efficiency = VL (I1 +I2+I4)-Pm/ VL (I1+I2+I4)

Plot the following graphs:-

(a) Output Vs Efficiency for Generator.

(b) Output Vs Efficiency for Motor.

NSCET LAB MANUAL


Genera-

Motor

Model graphs:-

η

O Output

Result:

NSCET LAB MANUAL


10.SEPARATION OF STRAY LOSSES IN A DC

MACHINE

Aim : To conduct the No-load Test at various speeds at two different excitations on a DC

shunt machine and to determine following losses:-

(a) Hysteresis Loss (b) Eddy Current Loss (c) Mechanical Loss.

Apparatus Required:



0-30V M C 1

2 Ammeter 0-5A 0-2A

M.C M.C

2 2


100/ 5A Wire wound 1

4 Connecting wires

5 Tachometer digital 0-9999 1


Circuit Diagram:

DPST FUSE

+

100Ω/5A

L A F

400Ω/1.7A

230 V

DC

Supply

+

(0-250V) V

−

+

A (0-5A)

− A

M

AA

+

A (0-2A)

−

F

FF

−

NSCET LAB MANUAL


Circuit diagram to find out Ra:

(0-30V)

Procedure:

1. Connected the circuit as per the circuit diagram.

2. Keep both field and armature rheostats at minimum position and start the

motor by using starter, and bring to rated speed by adjusting field rheostat.

3. Note down all the meter readings, repeat this by varying armature rheostat.

The field current to be kept constant.

4. Adjust the field to another suitable value and repeat step -3

5. Find the armature resistance by conducting the experiment.

Observations: Field current (if)=

S.

No

Armature

Voltage= Va

Armature

Current= Ia

Speed

N

Back

EMF Eb

Armature

input

Armature

Cu loss

Stray loss

DPST FUSE

+ +

100Ω/5A A (0-5A)

−

230 V

DC

Supply

A

M

AA

+

V

−

−

NSCET LAB MANUAL


Evaluation of friction, Hysterisis and Eddy current losses(Different speeds)

S. No Speed N

Friction loss AN+BN2

Hysterisis Loss CM

Eddy current loss DN2

Calculations:-

Stray losses (Ps)= Mechanical loss + Eddy current loss + Hysterisis loss

At constant normal excitation:

Ps=AN+BN2 +CN+DN2 ----------------------------- (1)

At constant reduced excitation

(Ps/N)=(A+C1)+(B+D1)N --------------------------------- (2)

Plot the graph between speeds Vs Ps/N

From the graph at two different speeds determine the values of Ps/N, for normal

and reduced excitations and find the values (A+C),(B+D),(A+C1) and (B+D1)

And from these values calculate the values of C-C1,D-D1.

The co-efficient of hysteresis loss C is proportional to 1.6, and the co-efficient of

eddy current loss D is proportional to 2. If and ’ are the fluxes corresponding

to the normal and reduced excitation ,the:-

(C’/C) = (’/)1.6

(D’/D) = (’/)2 at the same speed

Also,

(’/) = (E’,E) at any speed.

From the above equations evaluate the equations the constants A,B,C&D. Hence

evaluate the friction, Hysteresis and Eddy current losses at various speeds up to the

rated speed and tabulate the results in the table:-

NSCET LAB MANUAL


Model graphs:-

Y

Normal Excitation

PS / N

3/4 Excitation

O X

Speed (N)

Ps/N Vs N

Result

NSCET LAB MANUAL


11. Brake Test On DC Series Motor

AIM: To draw the performance characteristics of DC series motor by performing

Brake

APPARATUS:



2 Ammeter 0-20A M.C 1

3 Connecting wires

4 Tachometer 0-9999 digital 1


Circuit Diagram:

S1 S2

Fuse

+ DPST Switch

(0-20)A

MC

+ A

2 point starter

− L A

Y

+

230 V

DC

Supply

V

−

(0-250)V

MC A YY

M

AA

−

NSCET LAB MANUAL


THEORY : DC series motor is having high starting torque and its speed will be

decreases by increasing of load .series motor runs on load only. It implies that the

motor starts only when the load is applied on it. If S1, S2 are spring balance read-

ing force

T= (S1-S2)*G*r

r- brake drum radius

o/p power P=T*W

= 2πNT/60

Input power Pin =VIL

efficiency η = Pout/Pin*100

SPECIFICATION RATINGS OF DC SERIES MOTOR :

PROCEDURE:

1) Construct the circuit as shown in the figure

2) Apply some load and then switch on DPST switch

3) Take down the readings of N,S1,S2,IL

4) Calculate the efficiency under different loads

5) Plot the graph between o/p and i/p

Efficiency vs o/p

Torque vs IL

Speed vs IL

Speed vs T

PRECAUTIONS:

1) See that before switching on DPST whether some load is applied or not. If not

apply some load

2) Pour water on brake drum whenever you are changing the load

NSCET LAB MANUAL


TABLE:

S.NO. VOLTAGE LOAD

CURR

ENT

SPEED S1 S2 TORQUE P=2ΠNT/60

(out put

power)

Input

power

η =

Pout/

Pin

1) - - - -

-

- - - -

2) - - - -

-

- - - -

3) - - - -

-

- - - -

Model Graphs

Y

Ta

0

Ia

T

Tsh

X

NSCET LAB MANUAL


X

N

0 Ia Y

N vs Ia

Y

N vs T

Ta

NSCET LAB MANUAL


X

Y

η vs O/P

RESULT:

η

O/P

A

NSCET LAB MANUAL

12. Parallel Operation of Two DC Shunt Generators

DPST

230

V

3 point starter

L F A

F

F

400Ω/

1.7A

F

F

(0-20A)MC

+ −

A

A

(0-250V)MC

+ − V

S

DPD

OFF

(0-20A)MC

+ A −

A

A

A F

400Ω/

1.7A A

F M F

A

F F

230 V

DC

Suppl

Fus

Machine

Field REV Switch +

(0-250V)MC A

(0-20A)MC

Machine

Fuse

− V

+ −

Resistive load


G2 G1 M

NSCET LAB MANUAL


12. Parallel Operation of Two DC Shunt Generators

AIM:

To run two DC shunts generators in parallel and study the load sharing.

Apparatus:



2 Ammeter 0-20A M.C 3


4 Resistive Load 5 KW 1

5 DPDT Switch 2

6 SPST Switch 1

4 Connecting wires

5 Tachometer digital 1

PROCEDURE:

1. Ensure that the paralleling switch S1 is ‘OFF’ positions .open and the change

over switch S IS IN

2. Start machine NO1 and adjust the field excitation so that it generates the rated voltage and record the reading.

3. Put switch ‘S’ in the positon-1 and the gradually increase in the load in the

steps.

4. Note the load current of machine-1 and its terminal voltage.

5. Repeat the step [d] till the machine one is fully loaded.

6. Bring the load to zero and the stop the machine-1.

7. Put change over switch in ‘OFF’ position. Now start machine-2 and adjust the

voltage to rated value and repeat the steps done for machine-1.

8. Stop the machine and put the change over switch in ‘OFF’ position.

9. Run both machine keeping parallel switches S1 open.

10. Adjust the voltage each machine to its rated value and if the polarity is correct the

parallel volt meter V2 will read zero if not reverse the polarity of any one machine.

when parallel volt meter reads zero , close the parallel switch S1 by keeping the

NSCET LAB MANUAL


change over switch in either voltmeter reads zero , close the parallel switch S1 by

keeping the change over switch in either position 1or 2. Load the machine and note

down the individual machine load current, the total load current and the busbar

voltage.

11. Change the excitation of one of machine and observe the changes in ammeter

readings of each machine.

Observation Table:

S.no Generator 1 Generator 2 Gen1 & Gen 2 Parallel Total

Current

C, Bus

Bar vo

l

Voltage Current Voltage Current Load Current

Gen 1

Load Current

Gen 2

Result:

Documents

1. Magnetization Characteristics of DC Shunt … MANUAL/EM-I LAB MANUAL FINAL...NSCET LAB MANUAL DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING 1. Magnetization Characteristics